[PATCH v7 3/5] clk: Supply the critical clock {init, enable, disable} framework
Michael Turquette
mturquette at linaro.org
Thu Jul 30 16:35:30 PDT 2015
Quoting Lee Jones (2015-07-30 04:17:47)
> On Wed, 29 Jul 2015, Michael Turquette wrote:
>
> > Hi Lee,
> >
> > + linux-clk ml
> >
> > Quoting Lee Jones (2015-07-22 06:04:13)
> > > These new API calls will firstly provide a mechanisms to tag a clock as
> > > critical and secondly allow any knowledgeable driver to (un)gate clocks,
> > > even if they are marked as critical.
> > >
> > > Suggested-by: Maxime Ripard <maxime.ripard at free-electrons.com>
> > > Signed-off-by: Lee Jones <lee.jones at linaro.org>
> > > ---
> > > drivers/clk/clk.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
> > > include/linux/clk-provider.h | 2 ++
> > > include/linux/clk.h | 30 +++++++++++++++++++++++++++++
> > > 3 files changed, 77 insertions(+)
> > >
> > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > index 61c3fc5..486b1da 100644
> > > --- a/drivers/clk/clk.c
> > > +++ b/drivers/clk/clk.c
> > > @@ -46,6 +46,21 @@ static struct clk_core *clk_core_lookup(const char *name);
> > >
> > > /*** private data structures ***/
> > >
> > > +/**
> > > + * struct critical - Provides 'play' over critical clocks. A clock can be
> > > + * marked as critical, meaning that it should not be
> > > + * disabled. However, if a driver which is aware of the
> > > + * critical behaviour wants to control it, it can do so
> > > + * using clk_enable_critical() and clk_disable_critical().
> > > + *
> > > + * @enabled Is clock critical? Once set, doesn't change
> > > + * @leave_on Self explanatory. Can be disabled by knowledgeable drivers
> >
> > Not self explanatory. I need this explained to me. What does leave_on
> > do? Better yet, what would happen if leave_on did not exist?
> >
> > > + */
> > > +struct critical {
> > > + bool enabled;
> > > + bool leave_on;
> > > +};
> > > +
> > > struct clk_core {
> > > const char *name;
> > > const struct clk_ops *ops;
> > > @@ -75,6 +90,7 @@ struct clk_core {
> > > struct dentry *dentry;
> > > #endif
> > > struct kref ref;
> > > + struct critical critical;
> > > };
> > >
> > > struct clk {
> > > @@ -995,6 +1011,10 @@ static void clk_core_disable(struct clk_core *clk)
> > > if (WARN_ON(clk->enable_count == 0))
> > > return;
> > >
> > > + /* Refuse to turn off a critical clock */
> > > + if (clk->enable_count == 1 && clk->critical.leave_on)
> > > + return;
> >
> > How do we get to this point? clk_enable_critical actually calls
> > clk_enable, thus incrementing the enable_count. The only time that we
> > could hit the above case is if,
> >
> > a) there is an imbalance in clk_enable and clk_disable calls. If this is
> > the case then the drivers need to be fixed. Or better yet some
> > infrastructure to catch that, now that we have per-user struct clk
> > cookies.
> >
> > b) a driver knowingly calls clk_enable_critical(foo) and then regular,
> > old clk_disable(foo). But why would a driver do that?
> >
> > It might be that I am missing the point here, so please feel free to
> > clue me in.
>
> This check behaves in a very similar to the WARN() above. It's more
> of a fail-safe. If all drivers are behaving properly, then it
> shouldn't ever be true. If they're not, it prevents an incorrectly
> written driver from irrecoverably crippling the system.
Then this check should be replaced with a generic approach that refuses
to honor imbalances anyways. Below are two patches that probably resolve
the issue of badly behaving drivers that cause enable imbalances.
>
> As I said in the other mail. We can do without these 3 new wrappers.
> We _could_ just write a driver which only calls clk_enable() _after_
> it calls clk_disable(), a kind of intentional unbalance and it would
> do that same thing.
This naive approach will not work with per-user imbalance tracking.
> However, what we're trying to do here is provide
> a proper API, so we can see at first glance what the 'knowledgeable'
> driver is trying to do and not have someone attempt to submit a 'fix'
> which calls clk_enable() or something.
We'll need some type of api for sure for the handoff.
Regards,
Mike
From 3599ed206da9ce770bfafcfd95cbb9a03ac44473 Mon Sep 17 00:00:00 2001
From: Michael Turquette <mturquette at baylibre.com>
Date: Wed, 29 Jul 2015 18:22:45 -0700
Subject: [PATCH 1/2] clk: per-user clk prepare & enable ref counts
This patch adds prepare and enable reference counts for the per-user
handles that clock consumers have for a clock node. This patch warns if
an imbalance occurs while trying to disable or unprepare a clock and
aborts, leaving the hardware unaffected.
Signed-off-by: Michael Turquette <mturquette at baylibre.com>
---
drivers/clk/clk.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 898052e..72feee9 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -84,6 +84,8 @@ struct clk {
unsigned long min_rate;
unsigned long max_rate;
struct hlist_node clks_node;
+ unsigned int enable_count;
+ unsigned int prepare_count;
};
/*** locking ***/
@@ -600,6 +602,9 @@ void clk_unprepare(struct clk *clk)
return;
clk_prepare_lock();
+ if (WARN_ON(clk->prepare_count == 0))
+ return;
+ clk->prepare_count--;
clk_core_unprepare(clk->core);
clk_prepare_unlock();
}
@@ -657,6 +662,7 @@ int clk_prepare(struct clk *clk)
return 0;
clk_prepare_lock();
+ clk->prepare_count++;
ret = clk_core_prepare(clk->core);
clk_prepare_unlock();
@@ -707,6 +713,9 @@ void clk_disable(struct clk *clk)
return;
flags = clk_enable_lock();
+ if (WARN_ON(clk->enable_count == 0))
+ return;
+ clk->enable_count--;
clk_core_disable(clk->core);
clk_enable_unlock(flags);
}
@@ -769,6 +778,7 @@ int clk_enable(struct clk *clk)
return 0;
flags = clk_enable_lock();
+ clk->enable_count++;
ret = clk_core_enable(clk->core);
clk_enable_unlock(flags);
--
1.9.1
From ace76f6ed634a69c499f8440a98d4b5a54d78368 Mon Sep 17 00:00:00 2001
From: Michael Turquette <mturquette at baylibre.com>
Date: Thu, 30 Jul 2015 12:52:26 -0700
Subject: [PATCH 2/2] clk: clk_put WARNs if user has not disabled clk
From the clk_put kerneldoc in include/linux/clk.h:
"""
Note: drivers must ensure that all clk_enable calls made on this clock
source are balanced by clk_disable calls prior to calling this function.
"""
The common clock framework implementation of the clk.h api has per-user
reference counts for calls to clk_prepare and clk_disable. As such it
can enforce the requirement to properly call clk_disable and
clk_unprepare before calling clk_put.
Because this requirement is probably violated in many places, this patch
starts with a simple warning. Once offending code has been fixed this
check could additionally release the reference counts automatically.
Signed-off-by: Michael Turquette <mturquette at baylibre.com>
---
drivers/clk/clk.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 72feee9..6ec0f77 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2764,6 +2764,14 @@ void __clk_put(struct clk *clk)
clk->max_rate < clk->core->req_rate)
clk_core_set_rate_nolock(clk->core, clk->core->req_rate);
+ /*
+ * before calling clk_put, all calls to clk_prepare and clk_enable from
+ * a given user must be balanced with calls to clk_disable and
+ * clk_unprepare by that same user
+ */
+ WARN_ON(clk->prepare_count);
+ WARN_ON(clk->enable_count);
+
owner = clk->core->owner;
kref_put(&clk->core->ref, __clk_release);
--
1.9.1
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